Without limiting the scope of the invention, its background is described in connection with receptor tyrosine kinases.
The FMS-like tyrosine kinase 3 (FLT3) gene encodes a membrane bound receptor tyrosine kinase that affects hematopoiesis leading to hematological disorders and malignancies. See Drexler, H G et al. Expression of FLT3 receptor and response to FLT3 ligand by leukemic cells. Leukemia. 1996; 10:588-599; Gilliland, D G and J D Griffin. The roles of FLT3 in hematopoiesis and leukemia. Blood. 2002; 100:1532-1542; Stirewalt, D L and J P Radich. The role of FLT3 in hematopoietic malignancies. Nat Rev Cancer. 2003; 3:650-665. Activation of FLT3 receptor tyrosine kinases is initiated through the binding of the FLT3 ligand (FLT3L) to the FLT3 receptor which is expressed on hematopoietic progenitor and stem cells.
FLT3 is one of the most frequently mutated genes in hematological malignancies, present in approximately 30% of adult acute myeloid leukemia (AML). See Patel, J P et al. Prognostic relevance of integrated genetic profiling in acute myeloid leukemia. N Eng J Med. 2012; 366:1079-1089; Cancer Genome Atlas Research Network. Genomic and epigenetic landscapes of adult de novo acute myelod leukemia. N Eng J Med. 2013; 388: 2059-74. FLT3 mutations have been detected in approximately 2% of patients diagnosed with intermediate and high risk myelodysplastic syndrome (MDS). See S Bains, Luthra R, Medeiros L J and Zuo Z. FLT3 and NPM1 mutations in myelodysplastic syndromes: Frequency and potential value for predicting progression to acute myeloid leukemia. American Journal of Clinical Pathology. January 2011; 135:62-69; P K Bhamidipati, Daver N G, Kantarjian H, et al. FLT3 mutations in myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML). 2012. Journal of Clinical Oncology. Suppl; abstract 6597. Similar to MDS, the number of FLT3 mutations in patients with acute promyelocytic leukemia (APL) is less than 5%. The most common FLT3 mutations are internal tandem duplications (ITDs) that lead to in-frame insertions within the juxtamembrane domain of the FLT3 receptor. FLT3-ITD mutations have been reported in 15-35% of adult AML patients. See Nakao M, S Yokota and T Iwai. Internal tandem duplication of the FLT3 gene found in acute myeloid leukemia. Leukemia. 1996; 10:1911-1918; H Kiyoi, M Towatari and S Yokota. Internal Tandem duplication of the FLT3 gene is a novel modality of elongation mutation, which causes constitutive activation of the product. Leukemia. 1998; 12:1333-1337. A FLT3-ITD mutation is an independent predictor of poor patient prognosis and is associated with increased relapse risk after standard chemotherapy, and decreased disease free and overall survival. See FM Abu-Duhier, Goodeve A C, Wilson G A, et al. FLT3 internal tandem duplication mutations in adult acute myeloid leukemia define a high risk group. British Journal of Haematology. 2000; 111:190-195; H Kiyoi, T Naoe, Y Nakano, et al. Prognostic implication of FLT3 and N-RAS gene mutations in acute myeloid leukemia. Blood. 1999; 93:3074-3080. Less frequent are FLT3 point mutations that arise in the activation loop and gatekeeper region of the FLT3 receptor. The most commonly affected activation loop codon is aspartate 835 (D835). The most frequently mutated codon in the receptor gatekeeper region is phenylalanine 691 (F691). Nucleotide substitutions of the D835 and F691I residues occur in approximately 5-10% of adult acute myeloid leukemia patients. See Y Yamamoto, H Kiyoi and Y Nakano, et al. Activating mutation of D835 within the activation loop of FLT3 in human hematologic malignancies. Blood. 2001; 97:2434-2439; C Thiede, Steudal C, Mohr B, et al. Analysis of FLT3-activating mutations in 979 patients with acute myelogenous leukemia: association with FAB subtypes and identification of subgroups with poor prognosis. Blood. 2002; 99:4326-4335; U Bacher, Haferlach C, W Kern, et al. Prognostic relevance of FLT3-TKD mutations in AML: the combination matters—an analysis of 3082 patients. Blood. 2008; 111:2527-2537. Although less frequent than FLT3-ITD and FLT3-TKD mutations, the presence of both FLT3-ITD and FLT3-TKD mutations predicts for the highest rate of relapse and shortest overall survival. Dual mutations occur in approximately 2% of adult acute myeloid leukemia patients. See Schlenk et al. Mutations and treatment outcome in cytogenetically normal acute myeloid leukemia. 2008; 358:1909-1918.
The heightened frequency of constitutively activated mutant FLT3 in adult AML has made the FLT3 gene a highly attractive drug target in this tumor type. Several FLT3 inhibitors with varying degrees of potency and selectivity for the target have been or are currently being investigated and examined in AML patients. See T Kindler, Lipka D B, and Fischer T. FLT3 as a therapeutic target in AML: still challenging after all these years. Blood. 2010; 116:5089-102.
FLT3 kinase inhibitors known in the art include Lestaurtinib (also known as CEP 701, formerly KT-555, Kyowa Hakko, licensed to Cephalon); CHIR-258 (Chiron Corp.); EB10 and IMC-EB10 (ImClone Systems Inc.); Midostaurin (also known as PKC412, Novartis AG); Tandutinib (also known as MLN-518, formerly CT53518, COR Therapeutics Inc., licensed to Millennium Pharmaceuticals Inc.); Sunitinib (also known as SU11248, Pfizer USA); Quizartinib (also known as AC220, Ambit Biosciences); XL 999 (Exelixis USA, licensed to Symphony Evolution, Inc.); GTP 14564 (Merck Biosciences UK); AG1295 and AG1296; CEP-5214 and CEP-7055 (Cephalon). The following PCT International Applications and U.S. patent applications disclose additional kinase modulators, including modulators of FLT3: WO 2002/032861, WO 2002/092599, WO 2003/035009, WO 2003/024931, WO 2003/037347, WO 2003/057690, WO 2003/099771, WO 2004/005281, WO 2004/016597, WO 2004/018419, WO 2004/039782, WO 2004/043389, WO 2004/046120, WO 2004/058749, WO 2003/024969 and U.S Patent Application No. 2004/0049032. See also Levis M, K F Tse, et al. 2001 “A FLT3 tyrosine kinase inhibitor is selectively cytotoxic to acute myeloid leukemia blasts harboring FLT3 internal tandem duplication mutations.” Blood 98(3): 885-887; Tse K F, et al., Inhibition of FLT3-mediated transformation by use of a tyrosine kinase inhibitor. Leukemia. July 2001; 15 (7): 1001-1010; Smith, B. Douglas et al., Singlet agent CEP-701, a novel FLT3 inhibitor, shows biologic and clinical activity in patients with relapsed or refractory acute myeloid leukemia Blood, May 2004; 103: 3669-3676; Griswold, Ian J. et al., Effects of MLN518, A Dual FLT3 and KIT Inhibitor, on Normal and Malignant Hematopoiesis. Blood, November 2004; 104 (9): 2912-2918 [Epub ahead of print July 8]; Yee, Kevin W. H. et al., SU5416 and SU5614 inhibit kinase activity of wild-type and mutant FLT3 receptor tyrosine kinase. Blood, October 2002; 100(8): 2941-2949. O'Farrell, Anne-Marie et al., SU11248 is a novel FLT3 tyrosine kinase inhibitor with potent activity in vitro and in vivo. Blood, May 2003; 101(9): 3597-3605; Stone, R. M et al., PKC-412 FLT3 inhibitor therapy in AML: results of a phase II trials. Ann. Hematol. 2004; 83 Suppl 1:S89-90; and Murata, K. et al., Selective cytotoxic mechanism of GTP-14564, a novel tyrosine kinase inhibitor in leukemia cells expressing a constitutively active Fms-like tyrosine kinase 3 (FLT3). J Biol Chem. Aug. 29, 2003; 278 (35): 32892-32898 [Epub 2003 Jun. 18]; Levis, Mark et al., Small Molecule FLT3 Tyrosine Kinase Inhibitors. Current Pharmaceutical Design, 2004, 10, 1183-1193.
FLT3 inhibitors are classified as Type I or Type II inhibitors. These two classifications are distinguished based on their relative affinities and mechanism of binding to phosphorylated and non-phosphorylated receptor sites. Type I inhibitors recognize the active conformation of kinases. This conformation is conducive to phosphotransfer. Type I inhibitors are generally composed of a heterocyclic ring system. See Liu, Y and N Gray. Rational design of inhibitors that bind to inactive kinase conformations. Nature Chem. Biol. 2006; 2:358-354. Examples of Type I FLT3 inhbitiors include crenolanib and midostaurin. See Muralidhara C, Ramachandran A, Jain V. Crenolanib, a novel type I, mutant-specific inhibitor of class III receptor tyrosine kinases, preferentially binds to phosphorylated kinases. Cancer Research. 2012; 72 (8 Supplement): 3683; J Cools, et al. Prediction of resistance to small molecule FLT3 inhibitors: implications for molecularly targeted therapy of acute leukemia. Cancer Res. 2004; 64:6385-6389. Resistant mutations that render the kinase of the receptor tyrosine kinase constitutively phosphorylated could potentially be sensitive to type I inhibitors that have greater affinity for the phosphorylated kinase.
Type II inhibitors bind preferentially to the inactive conformation of kinases. This conformation is typically referred to as ‘DFG-out’ owing to the rearrangement of the motif. See J Zhang, Yang PL, and Gray NS. Targeting cancer with small molecule kinase inhibitors. Nature Reviews Cancer. 2009; 9:28-39. Inhibitors such as imatinib, sorafenib and nilotinib bind in the type II conformation. See P W Manley, Cowan-Jacob S W, Mestan J. Advances in the structural biology, design and clinical development of Bcr-Abl kinase inhibitors for the treatment of chronic myeloid leukemia. Biochim. Biophis. Acta. 2005; 1754:3-13; PT Wan, et al. Mechanism of activation of the RAF-ERK signaling pathway by oncogenic mutations of B-RAF. Cell. 2004; 116:855-867. Resistant mutations to Type II inhibitors render the kinase domain of the receptor tyrosine kinase constitutively phosphorylated. Type I inhibitors that target the phosphorylated kinase can overcome the resistance resulting from the treatment with Type II inhibitors, and therefore have potential use in treating diseases that harbor these resistance mutations.